SAT Math : Coordinate Geometry

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #11 : Psat Mathematics

Solve the equation for x and y.

x – y = 26/17

2x + 3y = 2

 

 

Possible Answers:

x = 3

y = 2

x = 85/112

y = –85/18

x = 112/85

y = –18/85

x = –18/85

y = 112/85

Correct answer:

x = 112/85

y = –18/85

Explanation:

Straightforward problem that presents two unknowns with two equations. The student will need to deal with the fractions correctly to get this one right. Other than the fraction the problem is solved in the exact same manner as the rest in this set. The graph below illustrates the solution.

Sat_math_165_09 

 

 

 

Example Question #11 : Psat Mathematics

What is the equation for a line with endpoints (-1, 4) and (2, -5)?

Possible Answers:

y = -3x + 1

y = 3x - 1

y = -x - 3

y = x + 3

Correct answer:

y = -3x + 1

Explanation:

First we need to find the slope. Slope (m) = (y2 - y1)/(x2 - x1). Substituting in our values (-5 - 4)/(2 - (-1)) = -9/3 = -3 so slope = -3. The formula for a line is y = mx +b. We know m = -3 so now we can pick one of the two points, substitute in the values for x and y, and find b. 4 = (-3)(-1) + b so b = 1. Our formula is thus y = -3x + 1

Example Question #131 : Lines

What is the equation of a line that goes through (4, 1) and (–2, –2)?

Possible Answers:

y = 1/2x – 1

y = 4x – 2

y = x + 4

y = 4x – 1/2

y = 2x – 1/2

Correct answer:

y = 1/2x – 1

Explanation:

We will find the equation using slope intercept form: y=mx+b

1. Use the two points to find the slope.

The equation to find the slope of this line using two points is:

Msp12021di7e9ga6058a1500004b461070aaf75f5c

  Therefore, m = 1/2, so the slope of this line is 1/2.

2. Now that we have the slope, we can use one of the points that were given to find the y intercept. In order to do this, substitute y for the y value of the point, and substitute x for the x value of the point.

Using the point (–2, –2), we now have: –2 = (1/2)(–2) + b.

Simplify the equation to solve for b. b = –1

3. In this line m = 1/2 and b = –1

4. Therefore, y = 1/2x –1

Example Question #521 : Geometry

What line goes through the points (1, 1) and (–2, 3)?

Possible Answers:

3x – 2y = 5

3x + 2y = 6

2x + 3y = 5

3x + 5y = 2

2x – 4y = 6

Correct answer:

2x + 3y = 5

Explanation:

Let P1 (1, 1) and P2 (–2, 3).

First, find the slope using m = rise ÷ run = (y2 – y1)/(x2 – x1) giving m = –2/3.

Second, substutite the slope and a point into the slope-intercept equation y = mx + b and solve for b giving b = 5/3.

Third, convert the slope-intercept form into the standard form giving 2x + 3y = 5.

Example Question #17 : Psat Mathematics

If angle A is 1/3 the size of angle B, then what is angle A?

 

Possible Answers:

43.1

27.4

30

22.5

45

Correct answer:

22.5

Explanation:

The answer is 22.5. 

From the image we can tell that angle a and angle b are complimentary

a + b = 90    and    3a = b

a + 3a = 90

a = 22.5

Example Question #3 : How To Find The Equation Of A Line

What is the equation of the line with a negative slope that passes through the y-intercept and one x-intercept of the graph y = –x2 – 2x + 8 ?

Possible Answers:

y = –2x + 8

y = –2x + 4

y = –4x + 4

y = –x + 8

y = –4x + 8

Correct answer:

y = –4x + 8

Explanation:

In order to find the equation of the line, we need to find two points on the line. We are told that the line passes through the y-intercept and one x-intercept of y = –x2 – 2x + 8.

First, let's find the y-intercept, which occurs where x = 0. We can substitute x = 0 into our equation for y.

y = –(0)2 – 2(0) + 8 = 8

The y-intercept occurs at (0,8).

To determine the x-intercepts, we can set y = 0 and solve for x.

0 = –x2 – 2x + 8

–x2 – 2x + 8 = 0

Multiply both sides by –1 to minimize the number of negative coefficients.

x+ 2x – 8 = 0

We can factor this by thinking of two numbers that multiply to give us –8 and add to give us 2. Those numbers are 4 and –2.

x+ 2x – 8= (x + 4)(x – 2) = 0

Set each factor equal to zero.

x + 4 = 0

Subtract 4.

x = –4

Now set x – 2 = 0. Add 2 to both sides.

x = 2

The x-intercepts are (–4,0) and (2,0).

However, we don't know which x-intercept the line passes through. But, we are told that the line has a negative slope. This means it must pass through (2,0).

The line passes through (0,8) and (2,0).

We can use slope-intercept form to write the equation of the line. According to slope-intercept form, y = mx + b, where m is the slope, and b is the y-intercept. We already know that b = 8, since the y-intercept is at (0,8). Now, all we need is the slope, which we can find by using the following formula:

m = (0 – 8)/(2 – 0) = –8/2 = –4

y = mx + b = –4x + 8

The answer is y = –4x + 8.

Example Question #11 : How To Find The Equation Of A Line

 

Possible Answers:

Correct answer:

Explanation:

Equation of line: ,    = slope,  = -intercept

Step 1) Find slope ():  rise/run    

Step 2) Find -intercept ():    

                                                      

                                                      

                                                       

Example Question #12 : How To Find The Equation Of A Line

Whast line goes through the points  and ?

Possible Answers:

Correct answer:

Explanation:

Let P_{1}=(1,3) and P_{2}=(7,5)

The slope is geven by:  m = (y_{2} - y_{1}) \div (x_{2} - x_{1})  so

Then we use the slope-intercept form of an equation;   so

And we convert 

 

to standard form.

Example Question #522 : Geometry

What is the equation of the line that passes through the points (4,7) and (8,10)?

Possible Answers:

Correct answer:

Explanation:

In order to find the equation of the line, we will first need to find the slope between the two points through which it passes. The slope, , of a line that passes through the points and is given by the formula below:

We are given our two points, (4,7) and (8,10), allowing us to calculate the slope.

Next, we can use point slope form to find the equation of a line with this slope that passes through one of the given points. We will use (4,7).

Multiply both sides by four to eliminate the fraction, and simplify by distribution.

Subtract from both sides and add twelve to both sides.

This gives our final answer:

Example Question #51 : Other Lines

Which line contains the following ordered pairs:

 and

Possible Answers:

\small y=-\frac{1}{4}x+\frac{7}{2}

\small y=-x+14

\small y=x+14

\small y=\frac{1}{4}x+\frac{7}{2}

Correct answer:

\small y=-\frac{1}{4}x+\frac{7}{2}

Explanation:

First, solve for slope.

\small m=\frac{\Delta y}{\Delta x}=\frac{2-4}{6-(-2)}=\frac{-2}{8}=-\frac{1}{4}

Then, substitute one of the points into the equation y=mx+b.

\small 2=(-\frac{1}{4})(6)+b

\small 2=(-\frac{3}{2})+b

\small b=2+\frac{3}{2}=\frac{7}{2}

This leaves us with the equation \small y=-\frac{1}{4}+\frac{7}{2}

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